Preparation and hydrogenation of schiff&#39;s bases



"@ nired drama This invention relates to the manufacture of N-arylN-alicyclic-p-phenylenediamines and to the manufacture of the Schillsbase intermediate. The invention particularly relates to the manufactureof N-phenyl-N-cyclohexyhpphenylenediamine.

An object of the invention is to provide an economical process for themanufacture of N-aryl-N'-alicyclic-pphenylenediamines. Another object isto provide a process for converting N-aryl-p-phenylenediamines toN-aryl- N alicyclic p-phenylenediamines in high yields. Satisfactorymethods for producing il-phenyl-p-phenylenediamine have beendescribedand this intermediate is readily available. Particular objects are toprovide a method for producing the Schifis base fromN-phenyl-pphenylenediamine and cyclohexanone in high yield and toprovide a method for reducing the Schiiis base Without purifying it.Other and further objects will be apparent from the descriptionfollowing.

The reductive alkylation of p-phenylenediamine has can well documented.However, contrary to statements in the patent literature that reductivealltylation of N- phenyl-p-phenylenediamine with cyclohexanone is asimple matter, this reaction proceeds poorly. Yields have been too lowto make the product economically attractive and competitive. This issurprising, especially since reductive alkyiation or" p-phenylenediamineand of N-cyclohexyl-pphenylenediaim'ne with cyclohexanone is indeed asimple matter under conditions heretofore described. Nevertheless, thereductive alkylation of N-phenyl-p-phenylenediamine has been singularlyunsuccessful until discovery of the critical combination of reactionvariables described herein.

The Schiifs base recation ultimately proved to be a crucial step buteven after preparing the Schifis base in a preliminary step, reductiongave low yields. It was discovered that the Schiffs base is extremelysensitive to moisture. This not only renders reductive alkylationinfeasible, necessitatirn alkylation and reduction in separate 7 steps,but requires formation of the Schiffs base in very high yield free frommoisture and precursers thereof if its isolation and purification are tobe avoided. Thus,

formation of appreciable Schiifs base and water during hydrogenation,where heating is inevitable, must be avoided. However, it was furtherdiscovered that heating one mole of N-phenyl-p-phenylenediarnine and atleast three, preferably four, moles of cyclohexanone while removingWater by 'azeotropic distillation gave essentially quantitative yieldsof t. e Schiffs base which productthen reduced readily without thenecessity of purifying it. Under these conditions the reactions can beeffected with very high concentrations of reactants, thereby making theoperation more economical. Moreover, hydrogenation of the Schiffs basesucceeds Without any diluent yielding a product only slighly inferior inassay and almost indistinguishable for its intended use from materialhydrogenated in a solvent.

While a solvent, as for example benzene, can be added if desired, theexcess of cyclohexanone is a satisfactory azeotroping agent. It is notnecessary to form the Schiiis base at the atmospheric boiling point ofcyclohexanone. Mild heating is sur'licient to effect condensation sothat azeotroping under pressures less than atmospheric is feasible andis preferred because it reduces side reactions 3,hl4,%7 Patented Dec.26, 1961 ice and reduces opportunity for thermal decomposition. Theoptimum temperature for conducting the reaction is about 90 C., thepressure being adjusted so as to maintain azeotroping at about thistemperature. Although not distillable, the Schii'ls base is stable overa wide temperature range but there is evidence that small quantities ofby-products which accompany its formation at temperatures above 90 C.poison the catalyst in the hydrogenation step. The yields ofhydrogenated product tended to decrease slowly but significantly as thetemperature at which the Schiifs base was formed increased from 90 to160 C.

After forming an essentially quantitative yield of the dry Schiffs base,thereduction is straightforward- It is preferred to distill off the bulkof the excess cyclohexanone and to add another solvent, as for example,isopropanol, benzene or methyl alcohol, although neither step isessential. All of the cyclohexanone may be removed by reduced pressuredistillation. If desired a solution be prepared for transporting,pumping and storage. The Schiffs base may be reduced using formic acidin the Leulrart reaction but more economically by catalytic reductionover nickel. The examples below will illustrate the invention in greaterdetail.

N-phenyl-p-phenyleuediamine, Ml. (3., Bl. 179- 181 C./ 1 mm., 50 partsby weight (0.27 molecular proportion) and 200 parts by weight of benzeneare added to a glass or glass-lined reactor fitted with thermometer,stirrer, water trap, condenser and outlet to vacuum pump. To the benzenesolution 82 parts by weight (0.83 molecular proportion) of cyclohexanoneare added and the mixture heated to refluxing temperature. Water beginsto collect in the trap when the pot temperature reaches 84 C. Heatingand stirring are continued for 2.8 hours at 88-89" C. during which timeapproximately 90% of the water expected from a quantitative conversioncollects in the trap. There is probably some holdup of water in theequipment because it was demonstrated by adding water to dry Schiifsbase and then hydrogenating that 5% and 10% of a mole of Water per moleof base reduced the yield of hydrogenated product approximately 8% and18% respectively.

The reaction mixture is then transferred to an autoclave, 4.1 parts byweight nickel catalyst prepared from nickel formate added and the vesselpurged several times with hydrogen at lbs/m Hydrogen pressure is thenincreased to 300 lbs/in. and the reaction mixture stirred and heated toC. The reaction continues at 130- C. over about 1.5 hours. The contentsof the autoclave are then filtered While hot to remove catalyst. Uponcooling the bulk of the product crystallizes from solution and isseparated by filtration. The benzene is removed from the filtrate bydistillation and the residue subjected to steam to remove furthervolatile constituents by steam distillation. The solid product remainingis recrystallized from heptane. A 96% yield of N-cyclohexyl-N'-phenyl-p-phenylenediamine, M.P. 115-117 C. is obtained. V

The reaction rate in the first step increases significantly uponincreasing the cyclohexanone ratio to four moles per mole of amine butfurther increase has no beneficial result. According to a preferredmodification, 73 parts by Weight (0.40 mole) ofN-phenyl-p-phenylenediamine and parts by weight (1.58 moles) ofcyclohexanone arecharged into a glass or glass-lined reactor fitted asdescribed above. Additional cyclohexanone, 13 parts by Weight (5.13mole) is added to the outlet side. of the water trap. The line to thepump leads through a dry ice-acetone trap.

The reaction mixture is heated to 85 C. and the pressure of the systemreduced to 135 mm. where refluxing starts. Water forms rapidly at first,then more slowly until after 60 minutes the theoretical quantity hasbeen collected, no additional Water being observed in the reflux. Thepressure is gradually reduced to 48 mm. While the temperature ismaintained at 80-85 C. Cyclohexanone, 81 parts (70% of the excesscharged) is then distilled from the reaction mixture at 78-80 C. under40- 50 mm. pressure. 7

The 75% (by weight) solution of the Schifis base in cyclohexanoneobtained by the above procedure is charged into an autoclave, dilutedwith 70 parts by weight of benzene to produce a 50% solution of theSchiifs base in the mixed solvent and 5.0 parts moisture-free Raneynickel added. The autoclave is purged twice with hydrogen under 100lbs/in. hydrogen and the contents heated to 135 C. Absorption ofhydrogen takes place at 135-150 C. for 45 minutes.

The reactor is cooled to 40-50 C., then opened and the solution filteredto remove catalyst. Benzene is removed by distillation and high boilingvolatile constituents removed by steam distillation The dark solid whichremains dispersed in the Water is collected on a filter and dried at 70C. The yield of N-cyciohexyl-Nphenyl-p-phenylenediamine is 95%. V

A particular advantage of the process is that use of distilledN-phenyl-p-phenylenediamine is unnecessary.

The crude reaction product resulting from catalytic re- I duction of4-nitrosodiphenylamine reacts satisfactorily. After separating thecatalyst by filtration and removing solvent, water of reaction and anyother distillable constituents from the filtrate, the crude residue maybe converted directly to the anil.- For example, to 72.9 parts by weightof crude N-phenyl-p-phenylenediamine obtained as described, 156 parts byweight of cyclohexanone are added. The stirred mixture is heated (orcooled) to a pot temperature of about 5060 C. The pressure is thenreduced to approximately 200 mm. Hg and heat applied until refluxingsets in (approximately 80 pot, 62 head temperature). The heat is thencut back and refluxing maintained by slowly reducing the pressure. Thecondensate consists of the azeotrope mixture of cyclohexanone and Water.The lower Water layer is collected while the ketone layer is recycled.The pressure is brought down to 50 mm. Hg during the stripping of thewater.

When all the water of reaction has been collected as evidenced byconstant pot and head temperatures, and a very slow or absent rate ofwater formation (reaction time about 50-60 min. from beginning of waterremoval) the excess cyclohexanone is stripped to a final condition of150 pot temperature at mm. Hg. The recovered ketone, 100% of the excessused, is saved for reuse in the next batch.

The crude anil weighs about 105 parts by weight. An.

equal weight of 2-propanol or l-butanol is then added and the solutioncharged to an autoclave along with Raney nickel which has been Washedfree of water with 2-propanol. The catalyst charge is 4% based on theWeight of Schifis base, 4.2 parts dry basis.

The clave is purged, brought up to 850 lbs/in. hydrogen pressure,agitation started and heat applied. A slow uptake of hydrogen occurs atabout 100 C. but the major portion of reaction occurs at about 140 C.The reaction mixture is maintained between 140150 C. until theabsorption of hydrogen ceases. It is then held at 150 C. until theabsorption of hydrogen ceases. It is then held at 150 C. to insurecomplete reaction. The autoclave contents are then cooled to about 90 C,the clave is vented and the contents filtered to remove the catalyst.The filter cake is Washed with 2-propanol and kept moist untiltransferred back to the clave or temporarily stored under Z-propanol.The autoclave con tents should be filtered hot to prevent precipitation.of the product.

The filtered product is distilled to remove solvent and small amounts ofhigher boiling material. The main portion of Z-propanol is removed atatmospheric pressure. When the pot temperature rises to about 125 thegradual application of vacuum to about 200 mm. Hg pressure will removethe majority of the remaining alcohol. The distillation is continued to150 C. pot ten";- perature at 20 mm. Hg. The pot residue is parts byWeight of N-cyclohexyl-N-phenyl-p-phenylenediamine, melting about C.

Other alicyclic ketones may be employed in the process, as for examplecyclopentanone and lower alkyl cyclohexanoncs providing at least oneortho position is unsubstituted. Examples of suitable alkylcyclohexanones comprise o methylcyclohexanone, p methylcyclohexanone, mmethylcyclohexanone, 2,4 dimethylcyclohexanone, 3,5 imethylcyclohexanoneand 2,4,5 trimethylcyclohexanone. Other N aryl p-phenylenediamines maybe used, as for example N-naphthyl-p-phenylenediamine. Cyclopentanone ismuch more sluggish in reaction than cyclohexanone but by the hereindescribed process it is possible to prepare the heretofor unknownN-cyclopentyl-N'-phenyl-ppbenylenediamine.

N-phenyl-p-phenylenediamine, MP. 75 C., B.P. 179-181 C./1 mm., 46 partsby Weight, and 84 parts by weight of cyclopentanone are added to a glassor glasslined reactor fitted with a thermometer, stirrer, Water trap,condenser and outlet to vacuum pump. The reaction mixture is heated toabout 95-100 C. and the pressure of the system reduced to inducerefluxing at this temperature. The condensate consists of an azeotropemixture of cyclopentanone and water. The reaction is continued until thetheoretical quantity of Water has been collected in the trap. The excesscyclopentanone is then distilled from tthe reaction mixture underreduced pressure, an equal weight of 2-propanol added and the solutiontransferred to an autoclave together with 5.0 parts of dry Raney nickelcatalyst. The autoclave is purged twice with hydrogen and the contentsheated to C. under hydrogen pressure of about 500 lbs./in. sorption ofhydrogen takes place at 135-155 C. for about 50 minutes. The reaction iscooled and the contents filtered to remove catalyst and the productallowed to crystallize from solution. The product, N-cyclopentyl-N'-phenyl-p-phenylenediamine, is a solid, MP. 76-77 C. analyzing 5.54%nitrogen as compared to 5.52% calculated for C H N This compound is amore efiective antioxidant for rubber thanN-cyclohexyl-N'-phenylp-phenylenediamine.

It is intended to cover all changes and modifications of the examples ofthe invention herein chosen for purposes of disclosure which do notconstitute departures from the spirit and scope of the invention.

What is claimed is: a

1. In the method of preparing N-phenyl and N-naphthylN-cycloalkyl-p-phenylenediamines by reacting the correspondingN-substituted p-phenylenediamine with a cycloalkanone and catalyticallyreducing the resulting Schifis base, the combination of steps whichcomprises heating a reaction mixture consisting of one molecularproportion of a member of the group consisting of N-phenyl-p-phenylenediamine and N-naphthyl-p-phenylenediamine, at leastthree molecular proportions of a cycloalkanone selected from the groupconsisting of cyclohexanone, cyclopentanone, methylcyclohexanone,2,4-dimethylcyclohexanone, 3,S-dimethylcyclohexanone and2,4,5-trimethylcyclohexanone and azeotroping agent selected from thegroup consisting of the aforesaid cycloalkanones in excess of the onemolecular proportion required for reaction and benzene, whileazeotropically distilling water from the reaction mixture below C., saidazeotropic distillation being continued until substantially thetheoretical amount of water produced in the formation of the Schiffsbase has been removed, then subjecting the dry undistilled compositeSchifts base to the action of molecular hydrogen in the presence of anickel hydrogenation catalyst and hydrogenating the carhon-nitrogendouble bond of the Schifis base.

2. In the method of preparing N-phenyl-N'-cyclohexyl-p-phenylenediaminesby reacting N-phenyl-p-phenylenediamine with cyclohexanone andcatalytically reducing the resulting Schiffs base, the combination ofsteps which comprises heating a reaction mixture consisting of onemolecular proportion of N-phenyl-p-phenylenediamine and at least fourmolecular proportions of cyclohexanone While azeotropically distillingWater from the reaction mixture under less than atmospheric pressure at80-100" C. as a cyclohexanone azeotrope, said azeotropic distillationbeing continued until the theoretical amount of water produced in theformation or" the Schifis base has been removed, then subjecting the dryundistilled composite Schiifs base to the action of molecular hydrogenin the presence of a nickel hydrogenation catalyst and hydrogenating toN-cyclohexyl-N'-phenyl-pphenylenediamine.

3. In the method of preparing N-phenyl-N'-cyclohexyl-p-phenylenediaminesby reacting N-phenyl-p-phenylenediamine With cyclohexanone andcatalytically reducing the resulting SchilTs base, the combination ofsteps which comprises heating a reaction mixture consisting of onemolecular proportion of N-phenyl-p-phenylenediamine and at least fourmolecular proportions of cyclohexanone while distilling below 150 C.under less than atmospheric pressure said distillation being continueduntil the theoretical amount of water produced in the formation of theSchiffs base has been removed as cyclohexanone azeotrope and the bulk ofthe cyclohexanone has been removed, adding solvent selected from thegroup consisting of lower alkanols and benzene in amount sutficient toform a solution then subjecting the solution of the dry undistilledcomposite Schifis base to the action of molecular hydrogen in thepresence of a nickel hydrogenation catalyst and hydrogenating toN-cyclohexylpentyl-p-phenylenediamines by reactingN-phenyl-p-phenylenediamine With cyclopentanone and catalyticallyreducing the resulting Schifis base, the combination of steps whichcomprises heating a reaction mixture consisting of one molecularproportion of N-phenyl-p-phcnylenediamine and at least four molecularproportions of cyclopentanone While distilling below C. under less thanatmospheric pressure said distillation being continued until thetheoretical amount of water produced in the formation of the Schifisbase has been removed as cyclopentanone azeotrope and the bulk of thecyclopentanone has been removed, adding solvent selected from the groupconsisting of lower alkanols and benzene in amount sufficient to form asolution then subjecting the solution of the dry undistilled compositeSchiffs base to the action of molecular hydrogen in the presence of anickel hydrogenation catalyst and hydrogenating to Ncyclopentyl-N-phenyl-p-phenylenediamine.

References Cited in the file of this patent UNITED STATES PATENTS1,945,576 Horst Feb. 6, 1934 2,217,630 Winans Oct. 8, 1940 2,393,889Cook et a1. June 29, 1946 2,533,723 Dombrow Dec. 12, 1950 2,583,729Deanesly Jan. 29, 1952 FOREIGN PATENTS 514,329 Great Britain Nov. 6,1939 568,230 Great Britain Mar. 26, 1945 716,239 Great Britain Sept. 29,1954 844,402 France Apr. 17, 1939 OTHER REFERENCES Baltzly et 211.:Journal of Organic Chemistry, vol. 16: No. 2; pages 174-176 (1951).

1. IN THE METHOD OF PREPARING N-PHENYL AND N-NAPHTHYLN''-CYCLOALKYL-P-PHENYLENEDIAMINES BY REACTING THE CORRESPONDINGN-SUBSTITUTED P-PHENYLENEDIAMINE WITH A CYCLOALKANONE AND CATALYTICALLYREDUCING THE RESULTING SCHIFF''S BASE, THE COMBINATION OF STEPS WHICHCOMPRISES HEATING A REACTION MIXTURE CONSISTING OF ONE MOLECULARPROPORTION OF A MEMBER OF THE GROUP CONSISTING OFNPHENYL-P-PHENYLENEDIAMINE AND N-NAPHTHYL-P-PHENYLENEDIAMINE, AT LEASTTHREE MOLECULAR PROPORTIONS OF CYCLOALKANONE SELECTED FROM THE GROUPCONSISTING OF CYCLOHEXANONE, CYCLOPENTANONE, METHYLCYCLOHEXANONE,2,4-DIMETHYLCYCLOHEXANEONE, 3,5-DIMETHYLCYCLOHEXANONE AND2,4,5-TRIMETHYLCYCLOHEXANONE AND AZEOTROPING AGENT SELECTED FROM THEGROUP CONSISTING OF THE AFORESAID CYCLOALKANONES IN EXCESS OF THE ONEMOLECULAR PROPORTION REQUIRED FOR REACTION AND BENZENE, WHILEAZEOTROPICALLY DISTILLING WATER FROM THE REACTION MIXTURE BELOW 150*C.,SAID AZEOROPIC DISTILLATION BEING CONTINUED UNTIL SUBSTANTIALLY THETHEORETICAL AMOUNT OF WATER PRODUCED IN THE FORMATION OF THE SCHIFF''SBASE HAS BEEN REMOVED, THEN SUBJECTING THE DRY UNDISTILLED COMPOSITESCHIFF''S BAST TO THE ACTION OF MOLECULAR HYDROGEN IN THE PRESENCE OF ANICKEL HYDROGENATION CATALYST AND HYDROGENATING THE CARBON-NITROGENDOUBLE BOND OF THE SCHIFF''S BASE.